Histopathologic Background for Resistance to Conventional Catheter Ablation of Common Atrial Flutter

Histopathologic examination of the cavotricuspid isthmus in which a large-tip catheter was necessary to achieve conduction block is presented. No thickened myocardium or prominent trabeculation was observed on the ablation line. A small cardiac vein extending through the isthmus across the ablation scar was detected. The remaining myocardial cells were distributed along the small cardiac vein. It is possible that the luminal blood flow of the small cardiac vein protects the surrounding atrial muscle from effective delivery of radiofrequency energy.